The present invention is directed to comminuted coal-water slurries as a medium for transporting coal over long distances. Furthermore, the invention is directed to surfactants that maintain coal particles in suspension at a high solids concentration.
In view of the economic dislocations over the past decade due to the sharp increases in the price of imported petroleum, importing countries are seeking ways of exploiting indigenous fuels. For example, the United States can transport coal to diverse parts of the country in an economical way, as by a network of pipelines carrying a coal-water slurry, provided that a sufficient weight percentage of solids is transportable in the slurry. Excessive amounts of water in the slurry result in at least two problems; energy is required to transport the water over the long pipeline distances and to separate the water from the coal in the slurry after the slurry reaches its destination. Surfactant choice is an important factor in a given slurry's pumpability and flowability.
Coal-water slurries of the prior art use a variety of surfactants. For example, in U.S. Pat. No. 4,217,109, entitled "Composition Comprising a Pulverized Purified Substance, Water, and a Dispersing Agent, and a Method for Preparing the Composition", issued to Siwersson et al on Aug. 12, 1980, the surfactants or dispersing agents of the slurry having up to a 60% solids concentration include polyelectrolytes, such as alkali metal or ammonium salts of polycarboxylic acids and polyacrylates. The maximum amount of solids that are pumpable in the ash-water slurry of "Aqueous Slurry of Ash Concentrate and Process for Producing Same", U.S. Pat. No. 4,094,810, issued to Thomas on June 13, 1978, is 60%. Surfactants disclosed in that patent include those consisting of a carboxylic acid salt, a sulfonate salt, a sulfate group, and a phosphate group. U.S. Pat. No. 4,088,453, "Production of Solid Fuel-Water Slurries", issued to Wiese et al on May 9, 1978, and U.S. Pat. No. 3,019,059, "Process for Conveying Carbonaceous Solids Through Conduits", issued to McMurtrie on Jan. 30, 1962, disclose ammonia and coal acids, respectively, as surfactants to improve the pumpability or reduce the viscosity of slurries.